Method of casting metal and cast article



Patented May 12, 1942 sans!) "STATES ,PATENT oFF-lcs DIETHOD OF CASTING METAL AND CASI A v walter F. wright, wyoming. om@ Application July 31, 1940, Serial No. 348353 (c1. zz-ss) 4 Claims.

This invention relates generally to the art of casting metal and is particularly directed to an improved method of casting steel gear and wheel blanks and articles of that general nature.

Many castings are faulty and unusable because they contain shrinkage cavities or pipes. Such faults occurring inside of a casting, sometimes are exposed after the rough article has been machined. and the labor which has been spent in the machine operations prior to the discovery v which are last to solidify. This happens because, as the copling begins along the walls of the metal and proceeds inwardly from these surfaces, metal is drawn from the portions which still remain fluid and thus, metal is drawn from .the inner parts toward the outer, so that. finally an empty space or pipe is left in the center. Although it is not constant, as a general rule, the shrinkage amounts toas much as 5 or 6 per cent.

' inner.

In the past it has been lthe practice to provide a plurality of risers or feed heads in suchvplaces that any decrease in volume was taken careof by molten metal drawn from one of the plurality of eed heads, the theory being that the nal shrinkage cavities or pipes would be in the risers. A casting on the order of a gear blank usually required a number of risers positioned around the rim-and another riser positioned near the center of the hub of the casting. If enough risers were used, it was found that the majority of the shrinkage cavities could be corrected by this method. But the correct placing and relative sizes of the different feed heads for one casting citen required much study and time. and in some instances, it was Afound impossible to place the feedheads where they were most needed. Then, too, unless the risers'were placed with extreme care with regard to their relative proportions, it was found that varying degrees of denseness prevailed in the casting.

It has been an object of the present inventor to provide a method of casting which provides a having a ,uniform and maximum density and one which is free from the shrinkage cavities described above, which method does not require the use of the riserfor feeder system on the rim above referredito; V

In the fulllmentofthis objective, it has been discovered that the casting Vmass should be arrangeds'othat it increasesfromthe outermost poronstotheinnermost. Accordinglyassolidiflcction takes place; that is, as the casting w ilask is formed to provide a riser chamber I'|-.

- on line 8 8 of Figure 2.

cools, the cooling occurs from the outer portion toward the inner portion; that is, retrogressively. As the metal in the outer portion cools or shrinks, it draws from the inner portion proceeding in 'this manner to a central riser from which the central portion of the casting or `the most massive portion draws metal in the nal cooling phase. Obviously, the less massive the casting portion is, the faster it will cool.

In this procedure, the mold is rotated and centrifugal force constantly presses the molten metal outwardly into the rim or marginb the casting. This,l plus the inwardly progressing cooling action, produces a metal casting which is solid throughout from the extremities to the central mass with 'a 'single central riser suiicing to supplement the metal last to shrink.

It is another object of this linventor to provide Y a casting having its mass arranged as set forth; that is, with the outer extremities of less mass than the inner. The mass of the casting increases uniformly from the outer portion to the Other objects and advantages of my invention will be more fully set forth in akdescription of the drawing, forming a part of this specification, in which: f

Figure 1 is a sectional view taken through a mold and casting embodying my invention.

Figure 2 is a plan view o f the rough finished' sectional view taken The casting shown in the drawing is a gear blank. For this kind of casting it is especially desirable to have an article which is of maximumv 4 and driven by means of a bevel gear 5. The

table may be supported on a bearing as at l.

The-mold, constructed according to the .usual i foundry practice. comprises a circular flask formed in two pieces which are connected at a horizontal Joint. The upper piece, referred to as l the cope ask, is indicatedjat 1, and-the lower piece, referred to as the drag flask, is indicated at l., The respective flasks have sand molds formed therein, indicated generally at 9. In this instance fa core Il is provided for theM`central openinginthegear blank.

As shown in Figure 1, the sand in thecope immediately after formation and prior to removal from the mold.v The casting comprises a hub portion I2, spokes I3 and a rim Il. The dotdash line I5, dividing the riser from the hub ofl the gear blank, denes the line through which a cut is made to separate the riser from thehub after the article is removed from the mold.

Regarding the article, it may be seen that in 4cross section the riser Il comprises a greater mass than the hub I2, the hub comprises a greater mass than the larger ends of the tapered spokes I3 and the smaller ends of the tapered spokes comprise a greater mass than' the rim I4. The mass as measured by cross sectional area, is increased approaching the center.` Figures 3 to 6, inclusive, illustrate this point.

In practice, with the mold prepared, the molten metal is poured. The lower section of the hub illls first, then the spokes and rim, and then the upper section of the hub. The pouring continues until the riser is filled and leveled off. Immediately after pouring, the mold is rotated rapidly. Under centrifugal force, the `molten metal is .thrown outwardly, radially toward the rim. As

the molten metal cools, the rim is first to completely solidify, since it has the smallest cross section of the casting. Solidiiication continues moving inwardly from the smaller sections toward the center of the casting. While the solidiilcation moves inwardly, the outward pressure ofr wheel blanks, using the same method, may be cast with the flange on the lower side'of the mold so that the flange is filled with vmolten metal before the rim is completely lled. Here, the flange is designed so that its cross sectional area is less than the rims area. g

It will be apparent to those that many other articles may be cast according to this method. Some articles which do not readily lend themselves to the necessary design, i. e.,

- a design having the mass increasing from the outer edges toward a central point, may be designed with their mass proportioned according to this invention`and after they are cast, machined to the wanted proportions. 'I'his latter method,'al

rthough more expensive, is well worth the added cost when it is necessary'to turn out a casting which has to be guaranteed against internal cavities. In' most instances, the extra machining is confined to the center sections and takes no more time to accomplish than 4it did to cut of! the many risers used in past methods.

Having described my invention, I claim:

l. The method of casting steel to provide an article of the type having a hub, a rim, and a connection portion, comprising; the steps of, providing -a mold in which lthe cross-sectional area This view may be treated as showing the casting of the mold cavity increases from the rim. portion to the hub portion, providing a riser cavity at the center of the mold to feed the central cavity thereof, and rotating the mold to cause the molten steel to be -urged outwardly whereby the steel solidifles at the rim portions first and solidication proceeds inwardly to the center portion,

which portion being the last to cool is fed from' of forced cooling and through normal dissipation of heat, as distinguished from artificial cooling or chilling, molten metal introduced into the mold cavity through'its central chamber and forced outwardly under centrifugal force to the rim and interconnecting chamber will solidify at a given point in any chamber and thereby close said chamber against further movement' of molten metal through it only after the metal-has solidined in the portions of the mold cavity which are more, remote from the central chamber. y

3. A method of casting steel or steel alloys which comprises preparing.a, sand mold devoid of chilling members or artificial cooling means, and providing in said mold a molding cavity which is made up of a' central chamber, a rim chamber and at least one chamber interconnecting the rim chamber and the central chamber,`

central chamber and ydelivered centrifugally to said rim chamber and interconnecting chamber will solidify throughout the cross-sectional area at any given point in any of said chambers only after the steel has solidified at points in said as the above described gear blank. Flanged car fluid state to serve as a reservoir supplying molten skilled in .the are chambers more remote from said central chamber whereby the steel in the central chamber is the steel last to cool and prior thereto remains in steel to offset the shrinkage attending the solidiiication of the steel-in the cavities remote from the central chamber, then introducing molten steel into said mold cavity through the central chamber and forcing saidmolten steel outwardly under centrifugal force whereby the metal solidifies retrogressively while under centrifugal force.

4. A steel casting of the type having a hub, a rim and a connecting portion, said casting formed in a sand mold of a shape providing a casting, the cross-sectional areas of which throughout the various portions increase gradually from the rim to the hub and formed of molten steel introduced into the entire mold cavity centrally thereof and forced outwardly centrifugally whereby the cooling takes place retrogressively from the rim por.. tion to the hub, and the steel in thehub portion is the last to cool and vprior thereto remains. in fluid state to serve as a reservoir supplying molten steel to oifset the 'shrinkage attending the solidiilcation of the steel in the cavities most remote from the hub portion. z

' WALTER I". WRIGHT. 

